The letter discovered at the end of the episode is an excerpt from West with the Night by Beryl Markham.
Echo & the Bunnymen | Echo of Moscow | Echo | Liverpool Echo | Echo Park | Dots Will Echo | Sunderland Echo | South Wales Echo | Southern Daily Echo | Lost in the Echo | Echo, Utah | Echo (phenomenon) | Echo Park, Los Angeles | Echo Orbiter | Echo (mythology) | Echo (music award) | Echo Arena Liverpool | ECHO | The Northern Echo | The Echo Maker | The Black Echo | L'Écho de Paris | Larry Echo Hawk | I'd Rather Shout at a Returning Echo than Kid Someone's Listening | Glen Echo Park (Maryland) | Glen Echo Park | Glen Echo, Maryland | Glen Echo | Evergreen (Echo & the Bunnymen album) | Evening Echo |